1. Field of the Invention
The present invention relates to a method for the contactless measuring of distance and position in respect of aircraft docking procedures, and also to an arrangement for that purpose.
2. Description of the Related Art
When docking an aircraft to a so-called gate-associated passenger bridge, it is known to measure the distance of the aircraft from the passenger bridge with the aid of a contactless measuring process. That measuring process is also applied in the case of so-called remote parking, i.e., when the aircraft is parked on the apron or on the hardstanding of a gate area instead of being docked with a passenger bridge. It is also known to indicate for the pilot the position of the aircraft in relation to the centerline along which the aircraft is to move toward a stop point, at which the door of the aircraft is located in registry with the opening of the passenger bridge, or in some other specific position. The distance measuring procedure is used to indicate the stop point to the pilot. The stop point is individual to different aircraft and is thus located at different distances from the distance measuring device used. Such a docking system is therefore aware of the type of aircraft to be docked and thereby also of the distance between the distance measuring device and a specific part of the aircraft.
It is necessary to measure that distance during the whole of the docking phase, in order to present the current distance on a display positioned in front of the pilot, such that the pilot will be able to judge the speed at which the aircraft approaches the stop point. Should the aircraft proceed beyond the stop point, there is a danger of, e.g., an aircraft wing or engine colliding with ground equipment, resulting in highly expensive repair work.
The technology most used at present for measuring that distance and, in certain instances, the position of the aircraft in relation to the centerline, employs the use of distance measuring lasers. Only a small number of companies are active within this field. Certain of them use that technology. The assignee of the present application, the Swedish company Safegate International AB, and RLG Corporation in the U.S. are among those companies that use that technology.
Honeywell and Siemens are examples of companies that use a video-based technique. The accuracy of a video camera is basically dependent on camera resolution and the measuring distance. Because it is necessary to rely on the contrast between the measured object and the surroundings when using the videobased technique, the result will be influenced by external factors, such as rain, fog, snow, and light conditions. The video technique is therefore less efficient.
The laser technique is superior to the video technique, among other reasons because the measurement obtained will be more exact, by virtue of being highly accurate per se, and also because the measuring points on the measured object, i.e., the aircraft, are small and the surroundings therefore have no real disturbing effect. Moreover, the absolute measuring accuracy does not vary appreciably with distance in the case of laser measuring processes.
However, there is a problem with existing docking systems in which lasers are used. According to international rules and regulations concerning existing equipment, the equipment should, itself, indicate when the measurements obtained are erroneous. No system that fulfils this requirement with complete satisfaction exists at present. This deficiency of existing systems presents a serious hazard, partly because an erroneous distance indication can be given, and partly because an erroneous indication is not presented to the pilot in control of a docking aircraft. Such defective functions in existing systems have resulted in incidents and accidents.
A known laser system is designed so that the distance measuring laser will measure the distance to a known reference for controlling measurement accuracy and function, for instance the distance to a reflector that is positioned in a direction from the laser that differs from the volume within which the laser measures against a docking aircraft. The laser is considered to have measured correctly, when the reference measurement is a distance that is in sufficient accord with the known distance. The measuring procedure is then undertaken solely toward an expected aircraft. The known system does not have the time to check measurement accuracy and function by measuring both against a reflector and carrying out measurements against an aircraft during a docking process at one and the same time. The inability of the known system to perform both of these tasks simultaneously is because the laser is adapted to scan a large number of measuring points in one or two dimensions within the measurement volume, whereas the reference measurement is carried out in a totally different direction. By measurement volume is meant the two-dimensional or three-dimensional space within which the laser scans by emitting respective received laser beams or rays.
Thus, when using this known system there is no knowledge of whether the laser measures the correct distance to an approaching aircraft, or even whether the system measures the distance at all. The laser light emitted may be absorbed by weather conditions that indicate to the laser that the measuring distance lies beyond its range.
The present invention solves this problem.
The present invention relates to a method for contactless measuring of distance to an aircraft when positioning the aircraft, such as when docking or parking the aircraft. A scanning laser associated with a distance measuring device is directed toward an area along a central line along which an aircraft is intended to be moved in positioning the aircraft, and is situated in front of an aircraft being positioned. The laser is adapted to emit measuring pulses stepwise at different angles to detect a predetermined measurement volume. The laser is calibrated with the distance from the laser to the ground in respect of at least some of the laser beam angles, and it measures the distance at those angles during positioning of an aircraft. The measured distances are compared with the calibrated distance in a computer associated with the distance measuring device. The laser is considered to measure the correct distance when predetermined agreement is reached.
The invention also relates to an arrangement for contactless measurement of the distance to aircraft in an aircraft positioning process, such as when docking or parking an aircraft.